<template>
	<ul class="list">
		<li class="item" 
			 v-for="item of letters" 
			 :key="item"
			 :ref="item"
			 @touchstart="handleTouchStart"
			 @touchmove="handleTouchMove"
			 @touchend="handleTouchEnd"
			 @click="handleLetterClick"
		>{{item}}</li>
	</ul>
</template>

<script>
export default{
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
		letters (){
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data (){
		return{
			touchStatus: false,//定义标识位
			startY: 0,
			timer: null
		}
	},
	updated (){
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e){
			this.$emit('change', e.target.innerText)
		},
		handleTouchStart (){
			this.touchStatus = true
		},
		handleTouchMove (e){
			if (this.timer) {
				clearTimeout(this.timer)
			}
			this.timer = setTimeout(() => {
				if (this.touchStatus) {
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY - this.startY) / 20)
					if (index >= 0 && index < this.letters.length) {
						this.$emit("change",this.letters[index])
					}
				}
			},16)
				
		},
		handleTouchEnd (){
			this.touchStatus = false
		}
	}
}
</script>

<style lang="stylus" scoped>
	@import "~styles/varibles.styl"
	.list
		display: flex
		flex-direction: column
		justify-content: center
		position: absolute
		top: 1.58rem
		right: 0
		bottom: 0
		width: .4rem
		.item
			line-height: .4rem
			text-align: center
			color: $bgColor
</style>